I just bought a used DJI RS3 from Amazon.

Opened it up, installed the app and connected to the gimbal but after that NOTHING happened. It didn't calibrate, firmware didn't update, I can't get the Gimbal to work.
Tried connecting to different phones, used the reset options in the menu. I have a red indicator in the top left of the Gimbal screen but it's not in the manual. The gimbal doesn't give me any errors but it seems, something is not right. Can I fix it or do I have to send it back?

I added a picture:

on the left you can see the red indicator on the Gimbal screen, also the phone showing 0% battery even though it's almost full. Then you can see that there is no proper input from the axis. And at last you see the Firmware Version isn't even shown.

Hi, fabiand. Thank you for reaching out. We'll forward your concern to our relevant team for further checking. We'll let you know once we receive an update.

Hi, fabiand. Thank you for patiently waiting. We now received feedback from our relevant team: The app shows "No ESC data", please perform an automatic gimbal check, restore the gimbal settings, and refresh the gimbal firmware. If the problem still exists, please send the product back to DJI for repair. You may submit an online repair request through this link: {https://repair.dji.com/repair/index}. If you need assistance with creating a ticket, you may contact DJI support at (https://www.dji.com/support). Hope this helps.